BREAST CANCER IS A multifactorial disease, meaning that it can arise from a number of different causes. For roughly 5 to 10 percent of people, it's the result of an inherited mutation on the BRCA1 or BRCA2 gene or another genetic mutation. "By simple math, some 90 percent of breast cancers happen because of other reasons," says Dr. J. Jaime Alberty, a breast surgical oncologist at the Dubin Breast Center at Mount Sinai Hospital and assistant professor of surgery at the Icahn School of Medicine at Mount Sinai in New York.

Environmental exposures, lifestyle, family history and personal history can all be factors, and because there's so many potential influences in the development of breast cancer over one's lifetime, it's difficult to point to a single thing as the cause of a specific case. But "we do know that there are things women can do to decrease their chances of getting breast cancer, such as a better lifestyle, a better diet and not being obese," he says.

Within those broad recommendations to reduce risk, doctors also advise limiting your exposure to carcinogens, or cancer-causing agents, in the environment. Chemicalsthat mimic the effects of estrogen, such as bisphenol-A, have recently garnered much attention for a potential link to breast cancer. There are other elements in the environment that might also increase risk of breast cancer, and some researchers are looking at whether radon is one of them.

The National Cancer Institute reports that "radon is a radioactive gas released from the normal decay of the elements uranium, thorium and radium in rocks and soil." It can diffuse into groundwater, too. It's odorless, tasteless, invisible and "does what radioactive things do, which is decay. It breaks down into new particles," says Dr. David P. Carbone, director of the Thoracic Center and professor of medicine at the Ohio State University James Cancer Hospital in Columbus. "One of those particles is called an alpha particle, which is a high-energy, heavy particle that can do a lot of DNA damage."

Because radon is a gas, it's easily breathed into the lungs, where it continues to decay, potentially altering your body's DNA repair mechanisms. This can lead to the development of cancerous tumors. "It's also possible to go other places in the body, and in fact it's around your body, too, so you can imagine that the breast is a target from that as well," Carbone says.

Alberty agrees that there could be a potential threat to breast cells from radon exposure as a matter of simple geography. "Theoretically, because the lungs and the breast are right next to each other and are neighbors anatomically speaking, it makes sense that radon could potentially cause these same DNA repair problems" that could develop into cancer.

However, "radon particles don't penetrate very far into tissue," Carbone says. This is why it's more likely to cause lung cancer than any other cancer, although an inconclusive link has also been drawn to some forms of leukemia. "When you breathe radon in, the gas is right there within a fraction of a millimeter of the cells that become a lung cancer. But in the breast, you have several millimeters of skin before you get to the breast cells that are the basis of breast cancer. So in theory, the risk of breast cancer would be less pronounced than that for lung."

Currently, there's very little evidence of any link between radon exposure and breast cancer. Much of what we currently know comes from a 2017 study conducted at the Harvard T.H. Chan School of Public Health. Using data from the massive cohort of more than 112,000 nurses who were enrolled in the Nurses' Health Study II, the Harvard researchers cross-referenced incidence of breast cancer with radon exposure maps. The study found no overall association between radon exposure and risk of developing breast cancer.

"To my knowledge, this was the first prospective study to analyze environmental radon exposure and the incidence of breast cancer," Alberty says. "Overall, there was no association between breast cancer risk and radon exposure and that's taking into account geography (radon levels vary by region), personal risk and types of breast cancer. However, when we do research in cancer, we're always looking at multi-variable analysis and we break down the different categories of possible criteria," he says. In drilling down further, the researchers did find a small association between triple-negative breast cancer in women who lived in places with the highest levels of radon.

There are a few different types of breast cancer. The most common are hormone-positive, in which the tumor uses the hormones estrogen and/or progesterone to grow. Some cancers also overexpress HER-2/neu, a growth hormone that can fuel tumor growth. However, about 15 percent of breast cancers do not use any of these hormones to fuel their growth. These more aggressive breast cancers are called triple-negative. Carbone says that the association found between radon exposure and triple-negative breast cancer in that 2017 study was "not statistically significant," but there was a potential link.

Reduce Radon Exposure for Overall Health

Whether you're worried about breast cancer or not, "the main message in my mind should be that radon is bad for you in many ways and high levels of radon are found in many residences, schools and public buildings. If you don't test for it, you won't know that you're being exposed," Carbone says.

Radon exposure has been conclusively linked to incidence of lung cancer. The Environmental Protection Agency estimates that about 20,000 cases of lung cancer a year in the United States are caused by radon exposure, making it the second biggest cause of lung cancer behind smoking. Smokers who are exposed to high levels of radon are at especially high risk.

"Radon levels vary by state, but we find radon in all 50 states," Alberty says. "It's something we can't control in the general environment," but it is controllable in the built-environment. The low-level exposure we all have daily when we're just living and breathing is not typically a problem. However, a build-up of radon gas that can accumulate in confined spaces is a concern that needs to be addressed.

Annie Cacciato, an Ohio resident and patient of Dr. Carbone's, believes her stage 4 lung cancer was caused by exposure to radon and says "radon is a real public health crisis" that needs to be addressed.

Although Cacciato knew to test her home, which she did and had it remediated when high levels were detected, she didn't know how much radon she was being exposed to all day while she was at work. Her high school also had high levels of radon, and over years of daily exposure, she developed lung cancer. A nonsmoker, Cacciato had few symptoms and was only diagnosed in 2013 after a bout of pneumonia proved difficult to shake. She is still undergoing treatment.

Although her diagnosis has been devastating, Cacciato has made it her mission to warn others of the dangers of radon exposure and to urge civic leaders to fund research and remediation programs that will lessen the general public's exposure to this known cancer-causing agent. "I'm trying to make something positive out of my experience," she says, choking back tears. "We just assume that living in the U.S., the best country in the world in 2018, that our air is safe to breathe. But it's not. It's up to every U.S. citizen to ensure that their air is safe to breathe."

She encourages everyone to have your homes, offices, schools and every other building you frequent tested for radon and to pursue mitigation if levels above 4 picocuries per liter of air are found. Remediation usually requires the assistance of a specially trained contractor, and you should get professional help to make sure it's being done right.

"People who spend a lot of time in the basement for work, people who work in mines and with building materials" and other people who may work or live in environments that don't have good ventilation should be especially concerned about the radon levels they're being exposed to, Alberty says. You can learn more about radon testing and how to get a testing kit from the EPA.

And be sure to test regularly. Radon levels in your home, office or school can change over time, so testing should become a semi-annual event that's just part of your overall home maintenance routine. "We have to make sure that our radon levels are safe, just like we know to change the battery in our smoke detectors," Cacciato says. "It's just something we've got to do for normal life maintenance – make sure your air is safe to protect yourself and your family."